Double-loop motion-compensation fine granular scalability

ABSTRACT

A video coding technique having motion compensation within a fine granular scalable coded enhancement layer. In one embodiment, the video coding technique involves a two-loop prediction-based enhancement layer including non-motion-predicted enhancement layer I- and P-frames and motion-predicted enhancement layer B-frames. The motion-predicted enhancement layer B-frames are computed using: 1) motion-prediction from two temporally adjacent differential I- and P- or P- and P- frame residuals, and 2) the differential B-frame residuals obtained by subtracting the decoded base layer B-frame residuals from the original base layer B-frame residuals. In a second embodiment, the enhancement layer further includes motion-predicted enhancement layer P-frames. The motion-predicted enhancement layer P-frames are computed using: 1) motion-prediction from a temporally adjacent differential I- or P-frame residual, and 2) the differential P-frame residual obtained by subtracting the decoded base layer P-frame residual from the original base layer P-frame residual.

RELATED APPLICATIONS

[0001] Commonly-assigned, copending U.S. Patent Application, No. ______,entitled “Single-Loop Motion-Compensation Fine Granular Scalability”,filed ______,2001.

[0002] Commonly-assigned, copending U.S. Patent Application, No._______, entitled “Totally Embedded FGS Video Coding with MotionCompensation”, filed _______, 2001.

FIELD OF THE INVENTION

[0003] The present invention relates to video coding, and moreparticularly to a scalable enhancement layer video coding scheme thatemploys motion compensation within the enhancement layer forbi-directional predicted frames (B-frames) and predicted frames andbidirectional predicted frames and (P- and B-frames).

BACKGROUND OF THE INVENTION

[0004] Scalable enhancement layer video coding has been used forcompressing video transmitted over computer networks having a varyingbandwidth, such as the Internet. A current enhancement layer videocoding scheme employing fine granular scalable coding techniques(adopted by the ISO MPEG-4 standard) is shown in FIG. 1. As can be seen,the video coding scheme 10 includes a prediction-based base layer 11coded at a bit rate R_(BL), and an FGS enhancement layer 12 coded atR_(EL).

[0005] The prediction-based base layer 11 includes intraframe coded Iframes, interframe coded P frames which are temporally predicted fromprevious I- or P-frames using motion estimation-compensation, andinterframe coded bi-directional B-frames which are temporally predictedfrom both previous and succeeding frames adjacent the B-frame usingmotion estimation-compensation. The use of predictive and/orinterpolative coding i.e., motion estimation and correspondingcompensation, in the base layer 11 reduces temporal redundancy therein.

[0006] The enhancement layer 12 includes FGS enhancement layer I-, P-,and B-frames derived by subtracting their respective reconstructed baselayer frames from the respective original frames (this subtraction canalso take place in the motion-compensated domain). Consequently, the FGSenhancement layer I-, P- and B-frames in the enhancement layer are notmotion-compensated. (The FGS residual is taken from frames at the sametime-instance.) The primary reason for this is to provide flexibilitywhich allows truncation of each FGS enhancement layer frame individuallydepending on the available bandwidth at transmission time. Morespecifically, the fine granular scalable coding of the enhancement layer12 permits an FGS video stream to be transmitted over any networksession with an available bandwidth ranging from R_(min)=R_(BL) toR_(max)=R_(BL)+R_(EL). For example, if the available bandwidth betweenthe transmitter and the receiver is B=R, then the transmitter sends thebase layer frames at the rate R_(BL) and only a portion of theenhancement layer frames at the rate R_(EL)=R−R_(BL). As can be seenfrom FIG. 1, portions of the FGS enhancement layer frames in theenhancement layer can be selected in a fine granular scalable manner fortransmission. Therefore, the total transmitted bit-rate isR=R_(BL)+R_(EL). Because of its flexibility in supporting a wide rangeof transmission bandwidth with a single enhancement layer.

[0007]FIG. 2 shows a block-diagram of a conventional FGS encoder forcoding the base layer 11 and enhancement layer 12 of the video codingscheme of FIG. 1. As can be seen, the enhancement layer residual offrame i (FGSR(i)) equals MCR(i)-MCRQ(i), where MCR(i) is themotion-compensated residual of frame i, and MCRQ(i) is themotion-compensated residual of frame i after the quantization and thedequantization processes.

[0008] Although the current FGS enhancement layer video coding scheme 10of FIG. 1 is very flexible, it has the disadvantage that its performancein terms of video image quality is relatively low compared with that ofa non-scalable coder functioning at the same transmission bit-rate. Thedecrease in image quality is not due to the fine granular scalablecoding of the enhancement layer 12 but mainly due to the reducedexploitation of the temporal redundancy among the FGS residual frameswithin the enhancement layer 12. In particular, the FGS enhancementlayer frames of the enhancement layer 12 are derived only from themotion-compensated residual of their respective base layer I-, P-, andB-frames, no FGS enhancement layer frames are used to predict other FGSenhancement layer frames in the enhancement layer 12 or other frames inthe base layer 11.

[0009] Accordingly, a scalable enhancement layer video coding scheme isneeded that employs motion-compensation in the enhancement layer toimprove image quality while preserving most of the flexibility andattractive characteristics typical to the current FGS video codingscheme.

SUMMARY OF THE INVENTION

[0010] The present invention is directed to an enhancement layer videocoding scheme, and in particular an FGS enhancement layer video codingscheme that employs motion compensation within the enhancement layer forpredicted and bidirectional predicted frames. One aspect of theinvention involves a method comprising the steps of: coding an uncodedvideo with a non-scalable codec to generate base layer frames; computingdifferential frame residuals from the uncoded video and the base layerframes, at least portions of certain ones of the differential frameresiduals being operative as references; applying motion-compensation tothe at least portions of the differential frame residuals that areoperative as references to generate reference motion-compensateddifferential frame residuals; and subtracting the referencemotion-compensated differential frame residuals from respective ones ofthe differential frame residuals to generate motion-predictedenhancement layer frames.

[0011] Another aspect of the invention involves a method comprising thesteps of: decoding a base layer stream to generate base layer videoframes; decoding an enhancement layer stream to generate differentialframe residuals, at least portions of certain ones of the differentialframe residuals being operative as references; applyingmotion-compensation to the at least portions of the differential frameresiduals operative as references to generate referencemotion-compensated differential frame residuals; adding the referencemotion-compensated differential frame residuals with respective ones ofthe differential frame residuals to generate motion-predictedenhancement layer frames; and combining the motion-predicted enhancementlayer frames with respective ones of the base layer frames to generatean enhanced video.

[0012] Still another aspect of the invention involves a memory mediumfor encoding video, which comprises code for non-scalable encoding anuncoded original video into base layer frames; code for computingdifferential frame residuals from the uncoded original video and thebase layer frames, at least portions of certain ones of the differentialframe residuals being operative as references; code for applyingmotion-compensation to the at least portions of the differential frameresiduals that are operative as references to generate referencemotion-compensated differential frame residuals; and code forsubtracting the reference motion-compensated differential frameresiduals from respective ones of the differential frame residuals togenerate motion-predicted enhancement layer frames.

[0013] A further aspect of the invention involves a memory medium fordecoding a compressed video having a base layer stream and anenhancement layer stream, which comprises: code for decoding the baselayer stream to generate base layer video frames; code for decoding theenhancement layer stream to generate differential frame residuals, atleast portions of certain ones of the differential frame residuals beingoperative as references; code for applying motion-compensation to the atleast portions of the differential frame residuals operative asreferences to generate reference motion-compensated differential frameresiduals; code for adding the reference motion-compensated differentialframe residuals with respective ones of the differential frame residualsto generate motion-predicted enhancement layer frames; and code forcombining the motion-predicted enhancement layer frames with respectiveones of the base layer frames to generate an enhanced video.

[0014] Still a further aspect of the invention involves an apparatus forcoding video, which comprises: means for non-scalable coding an uncodedoriginal video to generate base layer frames; means for computingdifferential frame residuals from the uncoded original video and thebase layer frames, at least portions of certain ones of the differentialframe residuals being operative as references; means for applyingmotion-compensation to the at least portions of the differential frameresiduals that are operative as references to generate referencemotion-compensated differential frame residuals; and means forsubtracting the reference motion-compensated differential frameresiduals from respective ones of the differential frame residuals togenerate motion-predicted enhancement layer frames.

[0015] Still another aspect of the invention involves an apparatus fordecoding a compressed video having a base layer stream and anenhancement layer stream, which comprises: means for decoding the baselayer stream to generate base layer video frames; means for decoding theenhancement layer stream to generate differential frame residuals, atleast portions of certain ones of the differential frame residuals beingoperative as references; means for applying motion-compensation to theat least portions of the differential frame residuals operative asreferences to generate reference motion-compensated differential frameresiduals; means for adding the reference motion-compensateddifferential frame residuals with respective ones of the differentialframe residuals to generate motion-predicted enhancement layer frames;and means for combining the motion-predicted enhancement layer frameswith respective ones of the base layer frames to generate an enhancedvideo.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The advantages, nature, and various additional features of theinvention will appear more fully upon consideration of the illustrativeembodiments now to be described in detail in connection withaccompanying drawings where like reference numerals identify likeelements throughout the drawings:

[0017]FIG. 1 shows a current enhancement layer video coding scheme;

[0018]FIG. 2 shows a block-diagram of a conventional encoder for codingthe base layer and enhancement layer of the video coding scheme of FIG.1;

[0019]FIG. 3A shows an enhancement layer video coding scheme accordingto a first exemplary embodiment of the present invention;

[0020]FIG. 3B shows an enhancement layer video coding scheme accordingto a second exemplary embodiment of the present invention;

[0021]FIG. 4 shows a block-diagram of an encoder, according to anexemplary embodiment of the present invention, that may be used forgenerating the enhancement layer video coding scheme of FIG. 3A;

[0022]FIG. 5 shows a block-diagram of an encoder, according to anexemplary embodiment of the present invention, that may be used forgenerating the enhancement layer video coding scheme of FIG. 3B;

[0023]FIG. 6 shows a block-diagram of a decoder, according to anexemplary embodiment of the present invention, that may be used fordecoding the compressed base layer and enhancement layer streamsgenerated by the encoder of FIG. 4;

[0024]FIG. 7 shows a block-diagram of a decoder, according to anexemplary embodiment of the present invention, that may be used fordecoding the compressed base layer and enhancement layer streamsgenerated by the encoder of FIG. 5; and

[0025]FIG. 8 shows an exemplary embodiment of a system which may be usedfor implementing the principles of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0026]FIG. 3A shows an enhancement layer video coding scheme 30according to a first exemplary embodiment of the present invention. Ascan be seen, the video coding scheme 30 includes a prediction-based baselayer 31 and a two-loop prediction-based enhancement layer 32.

[0027] The prediction-based base layer 31 includes intraframe coded Iframes, interframe coded predicted P-frames, and interframe codedbi-directional predicted B-frames, as in the conventional enhancementlayer video scheme presented in FIG. 1. The base layer I-, P- andB-frames may be coded using conventional non-scalable frame-predictioncoding techniques. (The base layer I-frames are of course notmotion-predicted.)

[0028] The two-loop prediction-based enhancement layer 32 includesnon-motion-predicted enhancement layer I- and P-frames andmotion-predicted enhancement layer B-frames. The non-motion-predictedenhancement layer I- and P-frames are derived conventionally bysubtracting their respective reconstructed (decoded) base layer I- andP-frame residuals from their respective original base layer I- andP-frame residuals.

[0029] In accordance with the present invention, the motion-predictedenhancement layer B-frames are each computed using: 1) motion-predictionfrom two temporally adjacent differential I- and P- or P- and P- frameresiduals (a.k.a. enhancement layer frames), and 2) the differentialB-frame residual obtained by subtracting the decoded base layer B-frameresidual from the original base layer B-frame residual. The differencebetween 2) the differential B-frame residual and 1) the B-frame motionprediction obtained from the two temporally adjacent motion-compensateddifferential frame residuals provide a motion-predicted enhancementlayer B-frame in the Enhancement Layer 32. Both the motion-predictedenhancement layer B frames resulting from this process and thenon-motion-predicted enhancement layer I- and P- frames may be codedwith any suitable scalable codec, preferably a fine granular scalable(FGS) codec as shown in FIG. 3A.

[0030] The video coding scheme 30 of the present invention improves thevideo image quality because it reduces temporal redundancy in theenhancement layer B-frames of the enhancement layer 32. Since theenhancement layer B-frames account for 66% of the total bit-rate budgetfor the enhancement layer 32 in an IBBP group of pictures (GOP)structure, the loss in image quality associated with performing motioncompensation only for the enhancement layer B-frames is very limited formost video sequences. (In conventional enhancement layer video codingschemes, a popular rate-control is mostly performed within theenhancement layer by allocating an equal number of bits to allenhancement layer I-, P-, and B-frames.)

[0031] Further, it is important to note that rate-control plays animportant role for achieving good performance with the video codingscheme of the present invention. However, even a simplistic approachwhich allocates the total bit-budget Btot for a GOP according toBtot=bI*No._I_frames+bP* No._P_frames+bB*No._B_frames, where bI>bP>bB,already provides very good results. Further note that a different numberof enhancement layer bits/bitplanes (does not have to be an integernumber of bits/bitplanes) can be considered for each enhancement layerreference frame used in the motion compensation loops. Moreover, ifdesired, only certain parts or frequencies within the enhancement layerreference frame need be incorporated in the enhancement layermotion-compensation loop.

[0032] The packet-loss robustness of the above scheme is similar to thatof the current enhancement layer coding scheme of FIG. 1: if an erroroccurs in a motion-predicted enhancement layer B-frame, this error willnot propagate beyond the next received I- or P-frame. Two packet-lossscenarios can occur:

[0033] If an error occurs in the motion-predicted enhancement layerB-frame, the error is confined to that B-frame;

[0034] If an error occurs in an enhancement layer I- or P-frame, theerror will not go beyond the (two) motion-predicted enhancement layerB-frames using these enhancement layer frames as references. Then,either one of the motion-predicted enhancement layer B-frames can bediscarded and frame-repetition applied or error concealment can beapplied using the other uncorrupted reference enhancement layer frame.

[0035]FIG. 4 shows a block-diagram of an encoder 40, according to anexemplary embodiment of the present invention, that may be used forgenerating the enhancement layer video coding scheme of FIG. 3A. As canbe seen, the encoder 40 includes a base layer encoder 41 and anenhancement layer encoder 42. The base layer encoder 41 is conventionaland includes a motion estimator 43 that generates motion information(motion vectors and prediction modes) from the original video sequenceand appropriate reference frame stored in memory 44. A first motioncompensator 45 in a first motion compensation loop 62, processes themotion information and generates motion-compensated base layer referenceframes (Ref(i)). A first subtractor 46 subtracts the motion-compensatedbase layer reference frames Ref(i) from the original video sequence togenerate motion-compensated residuals of the base layer frames MCR(i).The motion-compensated residuals of the base layer frames MCR(i) areprocessed by a discrete cosine transform (DCT) encoder 47, a quantizer48, and an entropy encoder 49 into a portion of a compressed base layerstream (base layer frames) from the original video sequence. The motioninformation generated by the motion estimator 43 is also combined, via amultiplexer 50, with the portion of the base layer stream processed bythe first subtractor 46, DCT encoder 47, quantizer 48 and entropyencoder 49. The quantized motion-compensated residual of the base layerframes MCR(I) generated at the output of the quantizer 48 aredequantized by an inverse quantizer 51, and then inverse DCT transformedvia an inverse DCT unit 52. This process generatesquantized-and-dequantized versions of the motion-compensated residualsof the base layer frames MCRQ(i), at the output of the inverse DCT 52.The quantized-and-dequantized motion-compensated residuals of the baselayer frames MCRQ(i) and their respective motion-compensated base layerreference frames Ref(i) are summed in an adder 53 to generate newreference frames that are stored in the first frame memory 44 and usedby the motion estimator 43 and motion compensator 45 for processingother frames.

[0036] Still referring to FIG. 4, the enhancement layer encoder 42,which preferably comprises an FGS enhancement layer encoder (as shown inFIG. 4), includes a second subtractor 54 that computes the differencebetween the motion-compensated residuals of the base layer frames MCR(i)and the quantized-and-dequantized motion-compensated residuals of thebase layer frames MCRQ(i) to generate differential I-, P-, and B-frameresiduals FGSR(i), which in the case of the I- and P-frame residuals,are the enhancement layer I- and P- frames. A frame flow control device55 is provided for enabling the differential I- and P-frame residuals tobe processed conventionally while the differential B-frame residuals areprocessed with motion-compensation in the enhancement layer inaccordance with the principles of the present invention. The frame flowcontrol device 55 accomplishes this task by causing the data flow at theoutput of the second subtractor 54 to stream in a different manner inaccordance with the type of frame that is outputted by the secondsubtractor 54. More specifically, differential I- and P-frame residualsgenerated at the output of the second subtractor 54 are routed by theframe control device 55 to an FGS encoder 61 (or like scalable encoder)for FGS coding using conventional DCT encoding followed by bit-plane DCTscanning and entropy encoding to generate a portion(non-motion-predicted enhancement layer I- and P-frames) of a compressedenhancement layer stream. The differential I- and P-frame residualsgenerated at the output of the second subtractor 54 are also routed to asecond frame memory 58 where they are used later on formotion-compensation. The differential B-frame residuals generated at theoutput of the second subtractor 54 are routed by the frame controldevice 55 to a third subtractor 60 and the second frame memory 58. Asecond motion compensator 59 in second motion compensation loop 63,reuses the motion information from the original video sequence (theoutput of the motion estimator 43 of the base layer encoder 41) and thedifferential I- and P-frame residuals stored in the second frame memory58, which are used as references, to generate referencemotion-compensated differential (I- and P- or P- and P-) frame residualsMCFGSR(i). Note that only a portion of each reference differential I-and P-frame residual e.g. several bit-planes, is required, although theentire reference differential frame residual can be used if desired. Thethird subtractor 60 generates each motion-predicted enhancement layerB-frame MCFGS(i) by subtracting the reference motion-compensateddifferential (I- and P- or P- and P-) frame residual MCFGSR(i) from itsrespective differential B-frame residual FGSR(i). The frame flow controldevice 55 routes the motion-predicted enhancement layer B-framesMCFGS(i) to the FGS encoder 61 for FGS coding using conventional DCTencoding followed by bit-plane DCT scanning and entropy encoding wherethey are added to the compressed enhancement layer stream.

[0037] As should now be apparent, the base layer remains unchanged inthe enhancement layer video coding scheme of FIG. 3A. Moreover, theenhancement layer I- and P-frames are processed in substantially thesame manner as in the current FGS video coding scheme of FIG. 1,therefore, these frames are not motion-predicted within the enhancementlayer. In the case of the motion-predicted enhancement layer B-frames,it should be apparent now that the signal to be coded in the enhancementlayer of the i^(th) frame MCFGS equals:

MCFGS(i)=FGSR(i)−MCFGSR(i)=MCR(i)−MCRQ(i)−MCFGSR(i)

[0038] where MCR(i) is the motion-compensated residual of frame i afterthe quantization and the dequantization processes, FGSR(i) issubstantially identical to the current FGS video coding scheme of FIG.1, i.e., FGSR(i) equals MCR(i)-MCRQ(i), and MCFGSR(i) is the referencemotion-compensated differential frame residual for frame (i). It shouldbe noted that enhancement layer B-frame processing method of the presentinvention merely requires an additional motion-compensation loop in theenhancement layer for providing motion-predicted enhancement layerB-frames.

[0039]FIG. 6 shows a block-diagram of a decoder 70, according to anexemplary embodiment of the present invention, that may be used fordecoding the compressed base layer and enhancement layer streamsgenerated by the encoder 40 of FIG. 4. As can be seen, the decoder 70includes a base layer decoder 71 and an enhancement layer decoder 72.The base layer decoder 71 includes a demultiplexer 75 which receives theencoded base layer stream and demultiplexes the stream into first andsecond data streams 76 and 77. The first data stream 76, which includesmotion information (motion vectors and motion prediction modes), isapplied to a first motion compensator 78. The motion compensator 78 usesthe motion information and base layer reference video frames stored inan associated base layer frame memory 79 to generate motion-predictedbase layer P- and B-frames that are applied to a first input 81 of afirst adder 80. The second data stream 77 is applied to a base layervariable length code decoder 83 for decoding, and to an inversequantizer 84 for dequantizing. The dequantized code is applied to aninverse DCT decoder 85 where the dequantized code is transformed intobase layer residual video I-, P- and B-frames which are applied to asecond input 82 of the first adder 80. The base layer residual videoframes and motion-predicted base layer frames generated by the motioncompensator 78 are summed in the first adder 80 to generate base layervideo I-, P-, and B-frames that are stored in the base layer framememory 79 and optionally outputted as a base layer video.

[0040] The enhancement layer decoder 72 includes an FGS bit-planedecoder 86 or like scalable decoder that decodes the compressedenhancement layer stream to generate at first and second outputs 73 and74 the differential I-, P-, and B-frame residuals which are respectivelyapplied to first and second frame flow control devices 87 and 91. Thefirst and second frame flow control devices 87 and 91 enable thedifferential I- and P-frame residuals to be processed differently fromthe differential B-frame residuals by causing the data flow at theoutputs 73 and 74 of the FGS bit-plane decoder 86 to stream in adifferent manner in accordance with the type of enhancement layer framethat is outputted by the decoder 86. The differential I- and P-frameresiduals at the first output 73 of the FGS bit-plane decoder 86 arerouted by the first frame control device 87 to an enhancement layerframe memory 88 where they are stored and used later on for motioncompensation. The differential B-frame residuals at the first output 73of the FGS bit-plane decoder 86 are routed by the first frame controldevice 87 to a second adder 92 and processed as will be explainedfurther on.

[0041] A second motion compensator 90 reuses the motion informationreceived by the base layer decoder 71 and the differential I- andP-frame residuals stored in the enhancement layer frame memory 88 togenerate reference motion-compensated differential (I- and P- or P- andP-) frame residuals, which are used for predicting enhancement layerB-frames. The second adder 92 sums each reference motion-compensateddifferential frame residual and its respective differential B-frameresidual to generate an enhancement layer B-frame.

[0042] The second frame control device 91 sequentially routes theenhancement layer I- and P-frames (the differential I- and P-frameresiduals) at the second output 74 of the FGS bit-plane decoder 86 andthe motion-predicted enhancement layer B-frames at the output 93 of thesecond adder 92 to a third adder 89. The third adder 89 sums theenhancement layer I,-, P-, and B-frames together with theircorresponding base layer I-, P-, and B-frames to generate an enhancedvideo.

[0043]FIG. 3B shows an enhancement layer video coding scheme 100according to a second exemplary embodiment of the present invention. Ascan be seen, the video coding scheme 100 of the second embodiment issubstantially identical to the first embodiment of FIG. 3A except thatthe enhancement layer P-frames in the two-loop prediction-basedenhancement layer 132 are motion-predicted like the enhancement layerB-frames.

[0044] The motion-predicted enhancement layer P-frames are computed in amanner similar to the enhancement B-frames i.e., each motion-predictedenhancement layer P-frame is computed using: 1) motion-prediction from atemporally adjacent differential I- or P-frame residual, and 2) thedifferential P-frame residual obtained by subtracting the decoded baselayer P-frame residual from the original base layer P-frame residual.The difference between 2) the differential P-frame residual and 1) theP-frame motion prediction obtained from the temporally adjacentmotion-compensated differential frame residual provide amotion-predicted enhancement layer P-frame in the Enhancement Layer 132.Both the motion-predicted enhancement layer P-and B-frames resultingfrom this process and the non-motion-predicted enhancement layerI-frames may be coded with any suitable scalable codec, preferably afine granular scalable (FGS) codec as shown in FIG. 3B.

[0045] The video coding scheme 100 of FIG. 3B provides furtherimprovements in the video image quality. This is because the videocoding scheme 100 reduces temporal redundancy in both the P- andB-frames of the enhancement layer 132.

[0046] The video coding schemes of the present invention can bealternated with the current video coding scheme of FIG. 1 for thevarious portions of a video sequence or for various video sequences.Additionally, switching between all three video coding schemes i.e.,current video coding scheme of FIG. 1 and the video coding schemesdescribed in FIGS. 3A and 3B, can be done based on channelcharacteristics and can be performed at encoding or at transmissiontime. Further the video coding schemes of the present invention achievea large gain in coding efficiency with only a limited increase incomplexity.

[0047]FIG. 5 shows a block-diagram of an encoder 140, according to anexemplary embodiment of the present invention, that may be used forgenerating the enhancement layer video coding scheme of FIG. 3B. As canbe seen, the encoder 140 of FIG. 5 is substantially identical to theencoder 40 of FIG. 4 (which is used for generating the enhancement layervideo coding scheme of FIG. 3A), except that the frame flow controldevice 55 used in the encoder 40 is omitted. The frame flow controldevice is not necessary in this encoder 140 because the differentialI-frame residuals are not processed with motion-compensation and thus,do not need to be routed differently from the differential P- andB-frame residuals in the enhancement layer encoder 142.

[0048] Hence, the differential I-frame residuals generated at the outputof the second subtractor 54 pass to an FGS encoder 61 for FGS codingusing conventional DCT encoding followed by bit-plane DCT scanning andentropy encoding to generate a portion (non-motion-predicted enhancementlayer I- frames) of a compressed enhancement layer stream. Thedifferential I-frame residuals also pass to a second frame memory 58along with the differential P-frame residuals where they are used lateron for motion-compensation. The differential P- and B-frame residualsgenerated at the output of the second subtractor 54 are also passed to athird subtractor 60. A second motion compensator 59 in second motioncompensation loop 63, reuses the motion information from the originalvideo sequence (the output of the motion estimator 43 of the base layerencoder 41) and the differential I- and P-frame residuals stored in thesecond frame memory 58, which are used as references, to generatereference motion-compensated differential (I or P) frame residualsMCFGSR(i) for motion-predicting enhancement layer P-frames and reference(I- and P- or P- and P-) frame residuals MCFGSR(i) for motion-predictingenhancement layer B-frames. The third subtractor 60 generates eachmotion-predicted enhancement layer P- or B-frame MCFGS(i) by subtractingthe reference motion-compensated differential (I or P) or (I- and P- orP- and P-) frame residual MCFGSR(i) from its respective differential P-or B-frame residual FGSR(i). The motion-predicted enhancement layer P-and B-frames MCFGS(i) then pass to the FGS encoder 61 for FGS codingusing conventional DCT encoding followed by bit-plane DCT scanning andentropy encoding where they are added to the compressed enhancementlayer stream.

[0049] As in the video coding scheme of FIG. 3A, the base layer remainsunchanged in the enhancement layer video coding scheme of FIG. 3B.Moreover, it should be noted that enhancement layer P- and B-frameprocessing method of the present invention merely requires an additionalmotion-compensation loop in the enhancement layer for providingmotion-predicted enhancement layer P-and B-frames.

[0050]FIG. 7 shows a block-diagram of a decoder 170, according to anexemplary embodiment of the present invention, that may be used fordecoding the compressed base layer and enhancement layer streamsgenerated by the encoder 140 of FIG. 5. As can be seen, the decoder 170of FIG. 7 is substantially identical to the decoder 70 of FIG. 6, exceptthat the frame flow control devices 87 and 91 used in the decoder 70 areomitted. The frame flow control devices are not necessary in thisdecoder 170 because the differential I-frame residuals are not processedwith motion-compensation and thus, do not need to be routed differentlyfrom the decoded differential P- and B-frame residuals in theenhancement layer decoder 172.

[0051] Accordingly, the differential I- and P-frame residuals at thefirst output 73 of the FGS bitplane decoder 86 pass to the enhancementlayer frame memory 88 where they are stored and used later on for motioncompensation. The differential P- and B-frame residuals at the secondoutput 74 of the FGS bit-plane decoder 86 pass to a second adder 92. Thedifferential I-frame residuals (enhancement layer I-frames hereinafter)at the second output 74 of the FGS bit-plane decoder 86 pass to a thirdadder 89, the purpose of which will be explained further on. The secondmotion compensator 90 reuses the motion information received by the baselayer decoder 71 and the differential I- and P-frame residuals stored inthe enhancement layer frame memory 88 to generate 1) referencemotion-compensated differential (I- and P- or P- and P-) frameresiduals, which are used for predicting enhancement layer B-frames, and2) reference motion-compensated differential (I-or P-) frame residuals,which are used for predicting enhancement layer P-frames. The secondadder 92 sums the reference motion-compensated differential frameresiduals with their respective differential B-frame residuals orP-frame residuals to generate enhancement layer B- and P-frames. Thethird adder 89 sums the enhancement layer I,-, P-, and B-frames togetherwith their corresponding base layer I-, P-, and B-frames to generate anenhanced video.

[0052]FIG. 8 shows an exemplary embodiment of a system 200 which may beused for implementing the principles of the present invention. Thesystem 200 may represent a television, a set-top box, a desktop, laptopor palmtop computer, a personal digital assistant (PDA), a video/imagestorage device such as a video cassette recorder (VCR), a digital videorecorder (DVR), a TiVO device, etc., as well as portions or combinationsof these and other devices. The system 200 includes one or morevideo/image sources 201, one or more input/output devices 202, aprocessor 203 and a memory 204. The video/image source(s) 201 mayrepresent, e.g., a television receiver, a VCR or other video/imagestorage device. The source(s) 201 may alternatively represent one ormore network connections for receiving video from a server or serversover, e.g., a global computer communications network such as theInternet, a wide area network, a metropolitan area network, a local areanetwork, a terrestrial broadcast system, a cable network, a satellitenetwork, a wireless network, or a telephone network, as well as portionsor combinations of these and other types of networks.

[0053] The input/output devices 202, processor 203 and memory 204 maycommunicate over a communication medium 205. The communication medium205 may represent, e.g., a bus, a communication network, one or moreinternal connections of a circuit, circuit card or other device, as wellas portions and combinations of these and other communication media.Input video data from the source(s) 201 is processed in accordance withone or more software programs stored in memory 204 and executed byprocessor 203 in order to generate output video/images supplied to adisplay device 206.

[0054] In a preferred embodiment, the coding and decoding employing theprinciples of the present invention may be implemented by computerreadable code executed by the system. The code may be stored in thememory 204 or read/downloaded from a memory medium such as a CD-ROM orfloppy disk. In other embodiments, hardware circuitry may be used inplace of, or in combination with, software instructions to implement theinvention. For example, the elements shown in FIGS. 4-7 may also beimplemented as discrete hardware elements.

[0055] While the present invention has been described above in terms ofspecific embodiments, it is to be understood that the invention is notintended to be confined or limited to the embodiments disclosed herein.For example, other transforms besides DCT can be employed, including butnot limited to wavelets or matching-pursuits. In another example,although motion-compensation is accomplished in the above embodiments byreusing motion data from the base layer, other embodiments of theinvention can employ an additional motion estimator in the enhancementlayer, which would require sending additional motion vectors. In stillanother example, other embodiments of the invention may employ motioncompensation in the enhancement layer for just the P-frames. These andall other such modifications and changes are considered to be within thescope of the appended claims.

What is claimed is:
 1. A method of coding video, comprising the steps of: coding an uncoded video with a non-scalable codec to generate base layer frames; computing differential frame residuals from the uncoded video and the base layer frames, at least portions of certain ones of the differential frame residuals being operative as references; applying motion-compensation to the at least portions of the differential frame residuals that are operative as references to generate reference motion-compensated differential frame residuals; and subtracting the reference motion-compensated differential frame residuals from respective ones of the differential frame residuals to generate motion-predicted enhancement layer frames.
 2. A method of coding video according to claim 1, further comprising the step of coding the motion-predicted enhancement layer frames with a scalable codec.
 3. A method of coding video according to claim 1, further comprising the step of coding the motion-predicted enhancement layer frames with a fine granular scalable codec.
 4. A method of coding video according to claim 1, wherein the motion-predicted enhancement layer frames in the subtracting step include motion-predicted enhancement layer B-frames, the reference motion-compensated differential frame residuals in the subtracting step include reference motion-compensated differential I- and P-frame residuals or reference motion-compensated differential P- and P-frame residuals, and the respective ones of the differential frame residuals in the subtracting step include differential B-frames.
 5. A method of coding video according to claim 4, wherein the motion-predicted enhancement layer frames in the subtracting step further include motion-predicted enhancement layer P-frames, the reference motion-compensated differential frame residuals in the subtracting step further include reference motion-compensated differential I-frame residuals or reference motion-compensated P-frame residuals, and the respective ones of the differential frame residuals in the subtracting step further include differential P-frames.
 6. A method of coding video according to claim 1, wherein the motion-predicted enhancement layer frames in the subtracting step include motion-predicted enhancement layer P-frames, the reference motion-compensated differential frame residuals in the subtracting step include reference motion-compensated differential I-frame residuals or reference motion-compensated P-frame residuals, and the respective ones of the differential frame residuals in the subtracting step include differential P-frames.
 7. A method of decoding a compressed video having a base layer stream and an enhancement layer stream, the method comprising the steps of: decoding the base layer stream to generate base layer video frames; decoding the enhancement layer stream to generate differential frame residuals, at least portions of certain ones of the differential frame residuals being operative as references; applying motion-compensation to the at least portions of the differential frame residuals operative as references to generate reference motion-compensated differential frame residuals; adding the reference motion-compensated differential frame residuals with respective ones of the differential frame residuals to generate motion-predicted enhancement layer frames; and combining the motion-predicted enhancement layer frames with respective ones of the base layer frames to generate an enhanced video.
 8. A method of decoding video according to claim 7, wherein the motion-predicted enhancement layer frames in the adding step consist of motion-predicted enhancement layer B-frames, the reference motion-compensated differential frame residuals in the adding step consist of reference motion-compensated differential I- and P-frame residuals or reference motion-compensated differential P- and P-frame residuals, and the respective ones of the differential frame residuals in the adding step consist of differential B-frames.
 9. A method of decoding video according to claim 7, wherein the motion-predicted enhancement layer frames in the adding step include motion-predicted enhancement layer B-frames, the reference motion-compensated differential frame residuals in the adding step include reference motion-compensated differential I- and P-frame residuals or reference motion-compensated differential P- and P-frame residuals, and the respective ones of the differential frame residuals in the adding step include differential B-frames.
 10. A method of decoding video according to claim 9, wherein the motion-predicted enhancement layer frames in the adding step further include motion-predicted enhancement layer P-frames, the reference motion-compensated differential frame residuals in the adding step further include reference motion-compensated differential I-frame residuals or reference motion-compensated P-frame residuals, and the respective ones of the differential frame residuals in the adding step further include differential P-frames.
 11. A method of decoding video according to claim 7, wherein the motion-predicted enhancement layer frames in the adding step include motion-predicted enhancement layer P-frames, the reference motion-compensated differential frame residuals in the adding step include reference motion-compensated differential I-frame residuals or reference motion-compensated P-frame residuals, and the respective ones of the differential frame residuals in the adding step include differential P-frames.
 12. A memory medium for encoding video, the memory medium comprising: code for non-scalable encoding an uncoded video into base layer frames; code for computing differential frame residuals from the uncoded video and the base layer frames, at least portions of certain ones of the differential frame residuals being operative as references; code for applying motion-compensation to the at least portions of the differential frame residuals that are operative as references to generate reference motion-compensated differential frame residuals; and code for subtracting the reference motion-compensated differential frame residuals from respective ones of the differential frame residuals to generate motion-predicted enhancement layer frames.
 13. A memory medium for encoding video according to claim 12, further comprising code for scalable encoding the motion-predicted enhancement layer frames.
 14. A memory medium for encoding video according to claim 12, further comprising code for fine granular scalable encoding the motion-predicted enhancement layer frames.
 15. A memory medium for encoding video according to claim 12, wherein the motion-predicted enhancement layer frames include motion-predicted enhancement layer B-frames, the reference motion-compensated differential frame residuals include reference motion-compensated differential I- and P-frame residuals or reference motion-compensated differential P- and P-frame residuals, and the respective ones of the differential frame residuals include differential B-frames.
 16. A memory medium for encoding video according to claim 15, wherein the motion-predicted enhancement layer frames further include motion-predicted enhancement layer P-frames, the reference motion-compensated differential frame residuals further include reference motion-compensated differential I-frame residuals or reference motion-compensated P-frame residuals, and the respective ones of the differential frame residuals further include differential P-frames.
 17. A memory medium for encoding video according to claim 12, wherein the motion-predicted enhancement layer frames include motion-predicted enhancement layer P-frames, the reference motion-compensated differential frame residuals include reference motion-compensated differential I-frame residuals or reference motion-compensated P-frame residuals, and the respective ones of the differential frame residuals include differential P-frames.
 18. A memory medium for decoding a compressed video having a base layer stream and an enhancement layer stream, the memory medium comprising: code for decoding the base layer stream to generate base layer video frames; code for decoding the enhancement layer stream to generate differential frame residuals, at least portions of certain ones of the differential frame residuals being operative as references; code for applying motion-compensation to the at least portions of the differential frame residuals operative as references to generate reference motion-compensated differential frame residuals; code for adding the reference motion-compensated differential frame residuals with respective ones of the differential frame residuals to generate motion-predicted enhancement layer frames; and code for combining the motion-predicted enhancement layer frames with respective ones of the base layer frames to generate an enhanced video.
 19. A memory medium for decoding a compressed video according to claim 18, wherein the motion-predicted enhancement layer frames include motion-predicted enhancement layer B-frames, the reference motion-compensated differential frame residuals include reference motion-compensated differential I- and P-frame residuals or reference motion-compensated differential P- and P-frame residuals, and the respective ones of the differential frame residuals include differential B-frames.
 20. A memory medium for decoding a compressed video according to claim 19, wherein the motion-predicted enhancement layer frames further include motion-predicted enhancement layer P-frames, the reference motion-compensated differential frame residuals further include reference motion-compensated differential I-frame residuals or reference motion-compensated P-frame residuals, and the respective ones of the differential frame residuals further include differential P-frames.
 21. A memory medium for decoding a compressed video according to claim 18, wherein the motion-predicted enhancement layer frames include motion-predicted enhancement layer P-frames, the reference motion-compensated differential frame residuals include reference motion-compensated differential I-frame residuals or reference motion-compensated P-frame residuals, and the respective ones of the differential frame residuals include differential P-frames.
 22. An apparatus for coding video, the apparatus comprising: means for non-scalable coding an uncoded video to generate base layer frames; means for computing differential frame residuals from the uncoded video and the base layer frames, at least portions of certain ones of the differential frame residuals being operative as references; means for applying motion-compensation to the at least portions of the differential frame residuals that are operative as references to generate reference motion-compensated differential frame residuals; and means for subtracting the reference motion-compensated differential frame residuals from respective ones of the differential frame residuals to generate motion-predicted enhancement layer frames.
 23. An apparatus for coding video according to claim 22, further comprising means for scalable coding the motion-predicted enhancement layer frames.
 24. An apparatus for coding video according to claim 22, further comprising means for fine granular scalable coding the motion-predicted enhancement layer frames.
 25. An apparatus for coding video according to claim 22, wherein the motion-predicted enhancement layer frames include motion-predicted enhancement layer B-frames, the reference motion-compensated differential frame residuals include reference motion-compensated differential I- and P-frame residuals or reference motion-compensated differential P- and P-frame residuals, and the respective ones of the differential frame residuals include differential B-frames.
 26. An apparatus for coding video according to claim 25, wherein the motion-predicted enhancement layer frames further include motion-predicted enhancement layer P-frames, the reference motion-compensated differential frame residuals further include reference motion-compensated differential I-frame residuals or reference motion-compensated P-frame residuals, and the respective ones of the differential frame residuals further include differential P-frames.
 27. An apparatus for coding video according to claim 22, wherein the motion-predicted enhancement layer frames include motion-predicted enhancement layer P-frames, the reference motion-compensated differential frame residuals include reference motion-compensated differential I-frame residuals or reference motion-compensated P-frame residuals, and the respective ones of the differential frame residuals include differential P-frames.
 28. An apparatus for decoding a compressed video having a base layer stream and an enhancement layer stream, the apparatus comprising: means for decoding the base layer stream to generate base layer video frames; means for decoding the enhancement layer stream to generate differential frame residuals, at least portions of certain ones of the differential frame residuals being operative as references; means for applying motion-compensation to the at least portions of the differential frame residuals operative as references to generate reference motion-compensated differential frame residuals; means for adding the reference motion-compensated differential frame residuals with respective ones of the differential frame residuals to generate motion-predicted enhancement layer frames; and means for combining the motion-predicted enhancement layer frames with respective ones of the base layer frames to generate an enhanced video.
 29. An apparatus for decoding a compressed video according to claim 28, wherein the motion-predicted enhancement layer frames include motion-predicted enhancement layer B-frames, the reference motion-compensated differential frame residuals include reference motion-compensated differential I- and P-frame residuals or reference motion-compensated differential P- and P-frame residuals, and the respective ones of the differential frame residuals include differential B-frames.
 30. An apparatus for decoding a compressed video according to claim 29, wherein the motion-predicted enhancement layer frames further include motion-predicted enhancement layer P-frames, the reference motion-compensated differential frame residuals further include reference motion-compensated differential I-frame residuals or reference motion-compensated P-frame residuals, and the respective ones of the differential frame residuals further include differential P-frames.
 31. An apparatus for decoding a compressed video according to claim 28, wherein the motion-predicted enhancement layer frames include motion-predicted enhancement layer P-frames, the reference motion-compensated differential frame residuals include reference motion-compensated differential I-frame residuals or reference motion-compensated P-frame residuals, and the respective ones of the differential frame residuals include differential P-frames. 